varlink.cli: allow --bridge and --activate in bridge mode
varlink.cli: allow --bridge and --activate in bridge mode

~~~
$ python -m varlink.cli --bridge "python -m varlink.cli -A 'varlink-certification --varlink=\$VARLINK_ADDRESS' bridge" info
Vendor: org.varlink
Product: Varlink Certification Suite
Version: 0.1
URL: http://varlink.org
Interfaces:
   org.varlink.service
   org.varlink.certification

$ python -m varlink.cli --bridge "python -m varlink.cli --bridge \"python -m varlink.cli -A 'varlink-certification --varlink=\\\$VARLINK_ADDRESS' bridge\" bridge" info
Vendor: org.varlink
Product: Varlink Certification Suite
Version: 0.1
URL: http://varlink.org
Interfaces:
   org.varlink.service
   org.varlink.certification
~~~

varlink/python-varlink,varlink/python-varlink