chore: migrate graalvm jobs to kokoro instance pool

[mpeddada1]

Notable Changes:

• Removed unused keystore settings.
• Replaced use of TRAMPOLINE_IMAGE environment variable with container_properties { docker_image ...}}
• Modified renovate bot settings to edit new docker_image property's value when a new version of java-shared-config is available.

[mpeddada1]

Removing the TRAMPOLINE_IMAGE is resulting in:

Traceback (most recent call last):
  File "/tmpfs/src/gfile/trampoline_v1.py", line 137, in 
    main()
  File "/tmpfs/src/gfile/trampoline_v1.py", line 125, in main
    image = os.environ['TRAMPOLINE_IMAGE']
  File "/usr/lib/python3.5/os.py", line 725, in __getitem__
    raise KeyError(key) from None
KeyError: 'TRAMPOLINE_IMAGE'
cleanup

[mpeddada1]

After migrating to instance pools and re-running the kokoro jobs, the graalvm checks are not showing any logs and failing within 26s.

[mpeddada1]

Stacktrace:

See 'docker run --help'.
/b/f/w/src/gfile/trampoline_cleanup.sh: line 5: sudo: command not found