Metadata: import any() from Compat
Metadata: read in clients.xml on every write

This ensures consistency between the in-memory representation of
clients.xml and the representation on disk. If we don't read our
writes immediately, there's a race condition when creating a new
client: If it asserts its profile or version before the FAM event from
the clients.xml edit is processed, then the clients doesn't appear to
exist yet, and Bcfg2 complains.
Tests: Fix tests after 9a6a231

The addition of the call to load_xml in 9a6a231 causes the test to
fail because load_xml() expects to read a clients.xml file.  The
actual actual open calls in write_xml are dummied out with Mock,
so no file is written, and thus cannot be read back.  This commit
dummies out the load_xml and adds some more asserts for good measure.
Merge pull request #141 from fennm/fix-unit-tests-after-9a6a231

Tests: Fix tests after 9a6a231