All capabilities, except for boot_mode, are read from instance_info.
This change makes instance_info.capabilities[boot_mode] work as well
and deprecates instance_info.deploy_boot_mode.
Note that the special handling of properties.capabilities[boot_mode]
is kept in this patch.
Change-Id: Ic2e7fd4c71b7a7bc2950d17f7e1bbdad73bbb8a7