qemuProcessCreatePretendCmd: Rework FIPS handling

qemuProcessCreatePretendCmd: Rework FIPS handling

This function - in contrast with qemuBuildCommandLine - merely
constructs our internal command representation of a domain. This
is then later compared against expected output. Or, this function
is used also in virConnectDomainXMLToNative(). But due to a copy
paste error this function, just like its image - has @forceFips
argument that if enabled forces FIPS, otherwise mimics FIPS state
in the host. If FIPS is enabled or forced the generated command
line is different to state in which FIPS is disabled. Problem is,
while this could be desired in the virConnectDomainXMLToNative()
case, this is undesirable in the test suite as it will produce
unpredicted results.
Solution to this is to rename argument to @enableFips to
specifically tell whether we expect command line to be build in
either of fashions and make virConnectDomainXMLToNative()
implementation fetch FIPS state and pass it to
qemuProcessCreatePretendCmd().

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>