assert: Replace asserts with validation function

Replace 2 asserts for number of arguments with exiting validateArgTypes
function, that raise a clear error instead of the cryptic assert.

Another assert was removed as the code already used validateArgTypes
just after it.

Change-Id: Ib18aab097352af7cd9ca292d7ebfc79e9113d2d8
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/29302
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>