Description of problem:
virt-v2v doesn't support convert guest with 1 interface type to another,eg:interface type bridge to network

Version-Release number of selected component (if applicable):
libguestfs-1.28.1-1.26.el7.x86_64
virt-v2v-1.28.1-1.26.el7.x86_64


How reproducible:
100%

Steps to Reproduce:
1.Check virt-v2v manual,only map network to network,bridge type to bridge.
# man virt-v2v
       -n in:out
       -n out
       --network in:out
       --network out
       -b in:out
       -b out
       --bridge in:out
       --bridge out
           Map network (or bridge) called "in" to network (or bridge) called "out".  If no "in:" prefix is
           given, all other networks (or bridges) are mapped to "out".

2.-n and -b can be used at the same time.


Actual results:
As description.

Expected results:
virt-v2v can convert guest with all types of interface to another type.

Additional info:
Previous virt-v2v can map all types of interface to network or bridge.
# man virt-v2v
       -n network | --network network
           Map all guest bridges or networks which don’t have a mapping in the configuration file to
           network.

           This option cannot be used in conjunction with --bridge.

       -b bridge | --bridge bridge
           Map all guest bridges or networks which don’t have a mapping in the configuration file to
           bridge.

           This option cannot be used in conjunction with --network.