tests: use valid machine types for snapshot tests

tests: use valid machine types for snapshot tests

In preparation to turn the 'machine' parameter into a property string.

parse_property_string checks for the regex, therefore the test-cases
with 'somemachine' and 'someothermachine' would fail.

To avoid that, replace 'somemachine' and 'someothermachine' with 'q35'
and 'pc' with sed:

sed -i 's/somemachine/q35/g'
sed -i 's/someothermachine/pc/g'

Signed-off-by: Markus Frank <m.frank@proxmox.com>
[FE: improve wording in commit message]
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>