Tests should depend on PIP instead of Yum

Unit tests now use pip to install the desired version of
pip.  Functional tests have been changed to use pip instead
of yum to install the desired version of pip.

Change-Id: I4ccc743385fb4258549c115e575c8834fd4d0561
Signed-off-by: Luis Pabon <lpabon@redhat.com>
Reviewed-on: http://review.gluster.org/5853
Reviewed-by: Peter Portante <pportant@redhat.com>