add SeedNodes to CConnman::Options

Summary:
Start of a series of changes to clean up the instantiation of connman
by decoupling the command line arguments.

This is backport of core PR10467

Test Plan:

make check

Reviewers: #bitcoin_abc, schancel

Reviewed By: #bitcoin_abc, schancel

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1746