Update .bonsai.yml to use entity.system.arm_version correctly

[espenaf]

Please change all arm versions in .bonsai.yml from:

    -  "entity.system.os == 'linux'"
    -  "entity.system.arch == 'armv7'"

To:

        - entity.system.os == 'linux'
        - entity.system.arch == 'arm'
        - entity.system.arm_version == '7'

See sensu/check-plugin-template#11 for details.