VMware: implement get_host_ip_addr

This patch fixes a regression caused by commit
1deb31f85a8f5d1e261b2cf1eddc537a5da7f60b. The function get_host_ip_addr
is used by the resource_tracker and if it is not implemented all resize
operations fail.

Also put back the check for missing host, user, password config options
in the driver constructor.

Closes-bug: #1356449

Change-Id: I4ba6a0f9c3b9c2ce0e1750f8414625235d01d422
Merge "VMware: implement get_host_ip_addr"