This commit substitutes the now-deprecated gosdc library for the newer
triton-go library. This is transparent from a user perspective, except
for the fact that key material can now be ommitted and requests can be
signed with an SSH agent. This allows for both encrypted keys and ECDSA
keys to be used.
In addition, a fix is made to not pass in an empty array of networks if
none are specified in configuration, thus honouring the API default of
putting instances with no explicit networks specified on the Joyent
public and internal shared networks.
d9ba951929