[COIL][Autotest] Part 1 of removing non-inclusive terms in server/hosts/*

Lots of master ssh --> main ssh changes. First step is going to be to change
the .ini and yaml's to have both options, then crrev.com/c/2568404 will follow

BUG=b:169251128
TEST="dummy_pass"

Change-Id: I89b6eda248240369d5fdac674dba3c154aba35ea
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/2593913
Reviewed-by: Greg Edelston <gredelston@google.com>
Commit-Queue: Derek Beckett <dbeckett@chromium.org>
Tested-by: Derek Beckett <dbeckett@chromium.org>
diff --git a/global_config.ini b/global_config.ini
index 504f8db..b77c557 100644
--- a/global_config.ini
+++ b/global_config.ini
@@ -260,7 +260,9 @@
 [AUTOSERV]
 # Set to True to take advantage of OpenSSH-based connection sharing. This would
 # have bigger performance impact when ssh_engine is 'raw_ssh'.
+# enable_master_ssh is being depricated in favor of enable_main_ssh.
 enable_master_ssh: True
+enable_main_ssh: True
 
 [PACKAGES]
 # in days