client.tools: Fix python 2.4 incompatible constructs

Only later I realized that the recent jenkins integration
scripts were using the python keyword 'with', illegal
in python 2.4. So, in order to keep our 2.4 pylint results
as clean as possible, I replaced the uses of the mentioned
keyword with legal 2.4 code.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
client.shared.backports_unittest: Supress pylint E0602

Python 2.4 systems won't have bin, but the unittest takes
this into account on such systems. It is safe to ignore it.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>