Revert "avoid TB for encoding in python3"

This reverts commit 886df517fa803b51386275baa26763d63fc7537e.
remove unused import "commands"
make run_command_print() compatible with python3
Add 'scl' builder option for software collection name

With a general 'scl' builder option, a software collection name can be
specified irrespective of the releaser used.  RsyncReleaser's own 'scl'
option has been deprecated in favour of using 'builder.scl' in
releasers.conf.
Allow builder to run in test mode on untagged project

Particularly useful when creating new projects and wanting to avoid
creating an initial tag, this allows `tito build --test --srpm` etc
to run without any tag.
Merge branch 'run_command_print' of https://github.com/xsuchy/tito into xsuchy-run_command_print
Fix print without newline for EL5.
Fix pep8 issues.
Merge branch 'xsuchy-run_command_print'
Merge pull request #122 from domcleal/scl-builder-arg

Add 'scl' builder option for software collection name
Merge branch 'test-without-tag' of https://github.com/domcleal/tito into domcleal-test-without-tag

Conflicts:
	test/functional/builder_tests.py
Raise error on failed run_command.

Lost this somehow in refactoring, but right now failed commands are silent.
Raise an exception and print the error details.

Restore behaviour where we can print command output on success if desired.

Fix a couple tests that were actually failing due to missing rsync dest.