pybind/mgr: use tox.ini envlist defaults when run via cmake

pybind/mgr: use tox.ini envlist defaults when run via cmake

Instead of having to remember there are two different envlists, one
default in tox.ini, one contained in CMakeLists.txt have CMakeLists.txt
simply reuse what is in tox.ini. Now, the python programmer who runs
`tox r` should not be surprised if something goes awry during `make
check` simply because `make check` was running a different set of
checks.

Signed-off-by: John Mulligan <jmulligan@redhat.com>