cephadm: compile cephadm

cephadm: compile cephadm

Compiling cephadm into an single binary offers the ability to split the
code from cephadm up into several files/modules. A side effect of having
a `cephadm.py` file (which, by renaming to cephadm.py has already become
a module) is that it can properly be imported and static type checking
inside `src/cephadm/tests/test_cephadm.py` is not an issue anymore.

Next steps would to split up cephadm into several modules and adapting
the test_cephadm.py import mechanism, as well as fixing the typing
issues, which are revealed by using a proper important statement.

Signed-off-by: Patrick Seidensal <pseidensal@suse.com>
Signed-off-by: John Mulligan <jmulligan@redhat.com>