Update the linux_load_command.py to support python3

[shahmishal]

No description provided.

[shahmishal]

@swift-ci test

[lorentey]

21:13:31 FAIL: swift-package-tests :: test-snapshot-binaries/linux_load_commands.py (14 of 31)
21:13:31 ******************** TEST 'swift-package-tests :: test-snapshot-binaries/linux_load_commands.py' FAILED ********************
21:13:31 Script:
21:13:31 --
21:13:31 : 'RUN: at line 3';   rm -rf /tmp/swift-integration-tests/test-snapshot-binaries/Output && mkdir -p /tmp/swift-integration-tests/test-snapshot-binaries/Output/linux_load_commands.py.tmp
21:13:31 : 'RUN: at line 4';   /usr/bin/python3 /home/buildnode/jenkins/workspace/pr-swift-integration-tests-linux/branch-main/swift-integration-tests/test-snapshot-binaries/linux_load_commands.py '/home/buildnode/jenkins/workspace/pr-swift-integration-tests-linux/latest_toolchain/swift-DEVELOPMENT-SNAPSHOT-2021-03-25-a-ubuntu16.04' '/tmp/swift-integration-tests/test-snapshot-binaries/Output' '/home/buildnode/jenkins/workspace/pr-swift-integration-tests-linux/latest_toolchain/swift-DEVELOPMENT-SNAPSHOT-2021-03-25-a-ubuntu16.04/usr/bin/llvm-readelf'
21:13:31 --
21:13:31 Exit Code: 1
21:13:31 
21:13:31 Command Output (stdout):
21:13:31 --
21:13:31 $ ":" "RUN: at line 3"
21:13:31 $ "rm" "-rf" "/tmp/swift-integration-tests/test-snapshot-binaries/Output"
21:13:31 $ "mkdir" "-p" "/tmp/swift-integration-tests/test-snapshot-binaries/Output/linux_load_commands.py.tmp"
21:13:31 $ ":" "RUN: at line 4"
21:13:31 $ "/usr/bin/python3" "/home/buildnode/jenkins/workspace/pr-swift-integration-tests-linux/branch-main/swift-integration-tests/test-snapshot-binaries/linux_load_commands.py" "/home/buildnode/jenkins/workspace/pr-swift-integration-tests-linux/latest_toolchain/swift-DEVELOPMENT-SNAPSHOT-2021-03-25-a-ubuntu16.04" "/tmp/swift-integration-tests/test-snapshot-binaries/Output" "/home/buildnode/jenkins/workspace/pr-swift-integration-tests-linux/latest_toolchain/swift-DEVELOPMENT-SNAPSHOT-2021-03-25-a-ubuntu16.04/usr/bin/llvm-readelf"
21:13:31 # command output:
21:13:31 Visiting lib: /home/buildnode/jenkins/workspace/pr-swift-integration-tests-linux/latest_toolchain/swift-DEVELOPMENT-SNAPSHOT-2021-03-25-a-ubuntu16.04/usr/lib/swift/linux/lib_InternalSwiftSyntaxParser.so
21:13:31 
21:13:31 # command stderr:
21:13:31 Traceback (most recent call last):
21:13:31   File "/home/buildnode/jenkins/workspace/pr-swift-integration-tests-linux/branch-main/swift-integration-tests/test-snapshot-binaries/linux_load_commands.py", line 161, in <module>
21:13:31     main()
21:13:31   File "/home/buildnode/jenkins/workspace/pr-swift-integration-tests-linux/branch-main/swift-integration-tests/test-snapshot-binaries/linux_load_commands.py", line 157, in main
21:13:31     process_library(args, l)
21:13:31   File "/home/buildnode/jenkins/workspace/pr-swift-integration-tests-linux/branch-main/swift-integration-tests/test-snapshot-binaries/linux_load_commands.py", line 88, in process_library
21:13:31     lines = list(reversed(subprocess.check_output([args.read_elf, "-program-headers", lib], universal_newlines=True).split("\n")[:-1]))
21:13:31   File "/usr/lib/python3.5/subprocess.py", line 626, in check_output
21:13:31     **kwargs).stdout
21:13:31   File "/usr/lib/python3.5/subprocess.py", line 693, in run
21:13:31     with Popen(*popenargs, **kwargs) as process:
21:13:31   File "/usr/lib/python3.5/subprocess.py", line 947, in __init__
21:13:31     restore_signals, start_new_session)
21:13:31   File "/usr/lib/python3.5/subprocess.py", line 1551, in _execute_child
21:13:31     raise child_exception_type(errno_num, err_msg)
21:13:31 FileNotFoundError: [Errno 2] No such file or directory: '/home/buildnode/jenkins/workspace/pr-swift-integration-tests-linux/latest_toolchain/swift-DEVELOPMENT-SNAPSHOT-2021-03-25-a-ubuntu16.04/usr/bin/llvm-readelf'
21:13:31 
21:13:31 error: command failed with exit status: 1
21:13:31 
21:13:31 --
21:13:31 
21:13:31 ********************