test_cephfs_shell: run cephfs-shell with conf file

test_cephfs_shell: run cephfs-shell with conf file

And set colors to False and debug to True in this conf file.

stdout captured by Python code in this testsuite can contain the colour
codes along with the expected string output. Setting colors to False in
cephfs-shell.conf should fix this.

Setting debug to False should help with analyzing test failures since
it enables printing messages that helps debugging (stacktrace for
cephfs-shell code, for example).

Signed-off-by: Rishabh Dave <ridave@redhat.com>