Ignore quotes in config file passed to sshuttle with @
Ignore quotes in config file passed to sshuttle with @

When users put parameters in a config file and pass them to sshuttle
using '@', they might copy the quotes from the command line into the
config file. This fix first ensures that we strip whitespace from the
beginning/end of each line in the config file. Then, if the line
begins and ends with a matching quote character, strip those too.

Fixes #573.

sshuttle/sshuttle,sshuttle/sshuttle