Make drydock case sensitive in attribute parsing

Summary: See D4047. Get rid of this strtolower() junk.

Test Plan:

$ /bin/drydock lease --type working-copy --attributes repositoryID=12
Acquired Lease 66

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2015

Differential Revision: https://secure.phabricator.com/D4048