feature: add configurable proxy_method to vhost and location resources

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
feature: add configurable proxy_set_body to vhost and location resources

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
simplified checks if variables are set in vhost_location_proxy template

kudos to Matthew Haughton for this suggestion

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
added specs for proxy_method and proxy_set_body

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
Merge pull request #170 from TelekomCloud/feature/set_proxy_method_and_body

Add support for proxy method and body