tests/acceptance: use "arch:" tag to filter target specific tests

Currently, some tests contains target architecture information, in the
form of a "x86_64" tag.  But that tag is not respected in the default
execution, that is, "make check-acceptance" doesn't do anything with
it.

That said, even the target architecture handling currently present in
the "avocado_qemu.Test" class is pretty limited.  For instance, by
default, it chooses a target based on the host architecture.

Because the original implementation of the tags feature in Avocado did
not include any time of namespace or "key:val" mechanism, no tag has
relation to another tag.  The new implementation of the tags feature
from version 67.0 onwards, allows "key:val" tags, and because of that,
a test can be classified with a tag in a given key.  For instance, the
new proposed version of the "boot_linux_console.py" test, which
downloads and attempts to run a x86_64 kernel, is now tagged as:

  🥑 tags=arch:x86_64

This means that it can be filtered (out) when no x86_64 target is
available.  At the same time, tests that don't have a "arch:" tag,
will not be filtered out.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20190312171824.5134-6-crosa@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

tests/acceptance/linux_initrd.py

@@ -19,7 +19,7 @@ class LinuxInitrd(Test):
     """
     Checks QEMU evaluates correctly the initrd file passed as -initrd option.
 
-    :avocado: tags=x86_64
+    :avocado: tags=arch:x86_64
     """
 
     timeout = 300