This patch adds hostdev test cases in qemuhotplugtest.c.

Note: the small tweak inside virpcimock.c was needed because
the new tests added a code path in which virHostHasIOMMU()
(virutil.c) started being called, and the mocked '/sys/kernel/'
prefix that is mocked in virpcimock.c wasn't being considered
in the opendir() mock. An alternative to avoid these situations
in virpcimock.c is implemented in the next patch.
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>
Signed-off-by: NShivaprasad G Bhat <sbhat@linux.vnet.ibm.com>
Signed-off-by: NDaniel Henrique Barboza <danielhb413@gmail.com>