Local certs management

[jbtrystram]

Keep the local certs in a known directory and use those by default .

drg create application foo # switches context to "foo"
drg trust init # stores local ca.key, uploads cert to application
drg create device device1 --certificate # creates device key/cert as test1.key/test1.crt and configures device
drg delete application foo
drg create create application
drg trust init --restore # uses local material
drg create device device1
drg trust import device1 # loads local key/cert