Deploy locks

Add a deploy lock for commands that are unsafe to run concurrently.

The lock is taken by creating a `mrsk_lock` directory on the primary
host. Details of who took the lock are added to a details file in that
directory.

Additional CLI commands have been added to manual release and acquire
the lock and to check its status.

```
Commands:
  mrsk lock acquire -m, --message=MESSAGE  # Acquire the deploy lock
  mrsk lock help [COMMAND]                 # Describe subcommands or one specific subcommand
  mrsk lock release                        # Release the deploy lock
  mrsk lock status                         # Report lock status

Options:
  -v, [--verbose], [--no-verbose]                # Detailed logging
  -q, [--quiet], [--no-quiet]                    # Minimal logging
      [--version=VERSION]                        # Run commands against a specific app version
  -p, [--primary], [--no-primary]                # Run commands only on primary host instead of all
  -h, [--hosts=HOSTS]                            # Run commands on these hosts instead of all (separate by comma)
  -r, [--roles=ROLES]                            # Run commands on these roles instead of all (separate by comma)
  -c, [--config-file=CONFIG_FILE]                # Path to config file
                                                 # Default: config/deploy.yml
  -d, [--destination=DESTINATION]                # Specify destination to be used for config file (staging -> deploy.staging.yml)
  -B, [--skip-broadcast], [--no-skip-broadcast]  # Skip audit broadcasts
```

If we add support for running multiple deployments on a single server
we'll need to extend the locking to lock per deployment.

test/cli/build_test.rb

@@ -15,8 +15,9 @@ class CliBuildTest < CliTestCase
   end
 
   test "push without builder" do
-    Mrsk::Cli::Build.any_instance.stubs(:create).returns(true)
+    stub_locking
     SSHKit::Backend::Abstract.any_instance.stubs(:execute)
+      .with { |arg| arg == :docker }
       .raises(SSHKit::Command::Failed.new("no builder"))
       .then
       .returns(true)
@@ -40,7 +41,9 @@ class CliBuildTest < CliTestCase
   end
 
   test "create with error" do
+    stub_locking
     SSHKit::Backend::Abstract.any_instance.stubs(:execute)
+      .with { |arg| arg == :docker }
       .raises(SSHKit::Command::Failed.new("stderr=error"))
 
     run_command("create").tap do |output|
@@ -69,4 +72,11 @@ class CliBuildTest < CliTestCase
     def run_command(*command)
       stdouted { Mrsk::Cli::Build.start([*command, "-c", "test/fixtures/deploy_with_accessories.yml"]) }
     end
+
+    def stub_locking
+      SSHKit::Backend::Abstract.any_instance.stubs(:execute)
+        .with { |arg1, arg2| arg1 == :mkdir && arg2 == :mrsk_lock }
+      SSHKit::Backend::Abstract.any_instance.stubs(:execute)
+        .with { |arg1, arg2| arg1 == :rm && arg2 == "mrsk_lock/details" }
+    end
 end