Speed up vagrant scheme calls by caching vagrant ssh-config

[shadyvb]

Hello!

This improves handling for vagrant scheme by caching the output of vagrant ssh-config, and using values within to convert the call to use the standard ssh scheme.

This helps speed up sample requests up to 3 seconds ( ie: sometimes 700% ) in all calls.

Before:

time wp --ssh=vagrant:default cli version                                                                                  WP-CLI 2.1.0
Connection to 127.0.0.1 closed.
        3.23 real         2.26 user         0.43 sys

time wp --ssh=vagrant:default option get siteurl                                                                          
https:///wordpress
Connection to 127.0.0.1 closed.
        4.14 real         2.27 user         0.44 sys

After:

time wp --ssh=vagrant:default cli version                                                                                  WP-CLI 2.1.0
        0.54 real         0.28 user         0.04 sys

time wp --ssh=vagrant:default option get siteurl                                                                          
https:///wordpress
        1.34 real         0.27 user         0.03 sys

Also fixed handling of vagrant connection URL so it behaves more consistently with the rest of connection types.

Fun irrelevant realization I couldn't resist to share: Shaving a minute a day off a developer's time, multiplied by 22 days a month, equals 22 minutes, multiplied by 30 developers a company, equals 11 hours a month, which is more than a billable day for agencies! And that doesn't even include the cost of interruptions!

[schlessera]

Thanks, @shadyvb, awesome improvement!