Tool, build_release: Return nonzero when builds fail

[theotherjimmy]

Description

It looks like this script will incorrectly report build failures and script
bugs as a pass. This patch should resolve that.

Pull request type

[x] Fix
[ ] Refactor
[ ] New target
[ ] Feature
[ ] Breaking change

[cmonr]

Small and simple.

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2254
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7148/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Test : SUCCESS

Build number : 2043
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7148/2043

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1879
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7148/

[0xc0170]

mbed 2 build failed, please review. I can see an error there, plus that it does not build anything build_mbed_libs() got an unexpected keyword argument 'verbose'

[theotherjimmy]

@0xc0170 Yeah, it needs a rebase after my other Mbed 2 PR.

[theotherjimmy]

Rebase done. Please review.

[cmonr]

/morph build

[cmonr]

Halting CI builds until RC3 PRs are completed. Will resume after.

[0xc0170]

/morph build

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2299
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7148/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 1921
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7148/

[mbed-ci]

Test : SUCCESS

Build number : 2075
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7148/2075

[cmonr]

@theotherjimmy @OPpuolitaival As far as y'all know, this is only used internally, correct? If so, this can be relabeled back to 5.9.1.