fix release robot issue for commit only tag

• if tag is not annotated, then it will be a commit object, instead of

creating a tag object

• don't check if ref object is tag, instead check if "tags" is in the

ref name

• change docstring to show how release_robot could be used as alternate

to versioneer, ie: copy and paste gist

https://gist.github.com/mikofski/e923750b415e4e4961b65a8eb42999e8#file-xyz__init__-py

• don't use contrib folder as default projdir, instead default to '.'
• return tag meta data if there is any from get_recent_tags() as tuple

(tag time, tag id, tag name) otherwise it's (None, None, None)

• remove test_tag_pattern from release_robot since it's in

test_release_robot()

• add tests

Signed-off-by: Mark Mikofski <mark.mikofski@sunpowercorp.com>