Add NVP advanced service check before deleting a router

Since NVP advanced services(LB/FW/VPN) are all routed inserted,
it is necessary to check service in use before deleting a router.
    *If there is one service inserted into the router, it would raise
RouterInUseByXXService error when deleting the router.

Change-Id: I9844f53918cad17cafde0783fe6b69cff246791d
Close-Bug: #1295494
NSX: Fix request_id in api_client to increment

Previously, the NSX request_id in the api_client would always be
0 because the current request id was stored in the class which is
always initialized on each request. This patch fixes that by storing
the request_id as a class variable.

Change-Id: I9ff4d3eb09899fe6d14b462dddf9daddbf77873b
Closes-bug: 1325100
Big Switch: fix capabilities retrieval code

References the raw REST response in the capabilities
parsing code so json.loads doesn't get an object
that may already be decoded and fail.

Closes-Bug: #1326173
Change-Id: Ia3179b7499f35a6ab2e9ce1631ab15ed27d64647
add engine parameter for offline migrations

Offline migration required config file containing connection string.
In that case only engine from URL was used. With this patch engine can be
passed from command line (or config file) along with plugins which sql
script will be generated accordingly.

DocImpact

Change-Id: Ib667a71960b833fd981f97fe7d6b1856084ef5c8
Closes-Bug: #1304326
Merge "NSX: Fix request_id in api_client to increment"
Merge "Add NVP advanced service check before deleting a router"
Merge "Big Switch: fix capabilities retrieval code"
Merge "add engine parameter for offline migrations"