Use a more stable method to detect rosdep changes

[cottsay]

The method for detecting rosdep changes in the repository checking system doesn't seem to work very well under all circumstances, and sometimes fails to determine the differences resulting in a failed job.

This change switches the test to use a line change detection mechanism already in use in another test, so it should be more stable.

Based on:

rosdistro/test/test_url_validity.py

Lines 314 to 330 in 0047072

	cmd = ('git config --get remote.%s.url' % UPSTREAM_NAME).split()
	try:
	remote_url = subprocess.check_output(cmd).decode('utf-8').strip()
	# Remote exists
	# Check url
	if remote_url != DIFF_REPO:
	detected_errors.append('%s remote url [%s] is different than %s' % (UPSTREAM_NAME, remote_url, DIFF_REPO))
	return detected_errors
	target_branch = '%s/%s' % (UPSTREAM_NAME, DIFF_BRANCH)
	except subprocess.CalledProcessError:
	# No remote so fall back to origin/master
	print('WARNING: No remote %s detected, falling back to origin master. Make sure it is up to date.' % UPSTREAM_NAME)
	target_branch = 'origin/master'
	cmd = ('git diff --unified=0 %s' % target_branch).split()
	diff = subprocess.check_output(cmd).decode('utf-8')

Reverts #30032
Should fix #29964

[hidmic]

LGTM

[ivanpauno]

Thanks for this @cottsay!

I see now failures that are reported in the wrong line, e.g. https://github.com/ros/rosdistro/pull/30565/files.
Is that related to this PR?

Maybe, there's a way to detect the changed lines comparing with master and then look up for the key names in the user branch to get the line numbers correctly (?).