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.

lib/mrsk/commander.rb

@@ -2,10 +2,11 @@ require "active_support/core_ext/enumerable"
 require "active_support/core_ext/module/delegation"
 
 class Mrsk::Commander
-  attr_accessor :verbosity
+  attr_accessor :verbosity, :lock_count
 
   def initialize
     self.verbosity = :info
+    self.lock_count = 0
   end
 
 
@@ -84,6 +85,9 @@ class Mrsk::Commander
     @traefik ||= Mrsk::Commands::Traefik.new(config)
   end
 
+  def lock
+    @lock ||= Mrsk::Commands::Lock.new(config)
+  end
 
   def with_verbosity(level)
     old_level = self.verbosity
@@ -97,14 +101,6 @@ class Mrsk::Commander
     SSHKit.config.output_verbosity = old_level
   end
 
-
-  # Test-induced damage!
-  def reset
-    @config = nil
-    @app = @builder = @traefik = @registry = @prune = @auditor = nil
-    @verbosity = :info
-  end
-
   private
     # Lazy setup of SSHKit
     def configure_sshkit_with(config)