qubes/vm: fix TemplateVM.commit_changes
qubes/vm: fix TemplateVM.commit_changes

Storage method was renamed to just `commit`, as it applies not only to
templates now.

marmarek/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin