Minimise holding the deploy lock

If we get an error we'll only hold the deploy lock if it occurs while
trying to switch the running containers.

We'll also move tagging the latest image from when the image is pulled
to just before the container switch. This ensures that earlier errors
don't leave the hosts with an updated latest tag while still running the
older version.

lib/mrsk/cli/base.rb

@@ -77,22 +77,32 @@ module Mrsk::Cli
       end
 
       def with_lock
-        acquire_lock
+        if MRSK.holding_lock?
+          yield
+        else
+          acquire_lock
 
-        yield
+          begin
+            yield
+          rescue
+            if MRSK.hold_lock_on_error?
+              error "  \e[31mDeploy lock was not released\e[0m"
+            else
+              release_lock
+            end
 
-        release_lock
-      rescue
-        error "  \e[31mDeploy lock was not released\e[0m" if MRSK.lock_count > 0
-        raise
+            raise
+          end
+
+          release_lock
+        end
       end
 
       def acquire_lock
-        if MRSK.lock_count == 0
-          say "Acquiring the deploy lock"
-          on(MRSK.primary_host) { execute *MRSK.lock.acquire("Automatic deploy lock", MRSK.config.version) }
-        end
-        MRSK.lock_count += 1
+        say "Acquiring the deploy lock"
+        on(MRSK.primary_host) { execute *MRSK.lock.acquire("Automatic deploy lock", MRSK.config.version) }
+
+        MRSK.holding_lock = true
       rescue SSHKit::Runner::ExecuteError => e
         if e.message =~ /cannot create directory/
           invoke "mrsk:cli:lock:status", []
@@ -103,10 +113,19 @@ module Mrsk::Cli
       end
 
       def release_lock
-        MRSK.lock_count -= 1
-        if MRSK.lock_count == 0
-          say "Releasing the deploy lock"
-          on(MRSK.primary_host) { execute *MRSK.lock.release }
+        say "Releasing the deploy lock"
+        on(MRSK.primary_host) { execute *MRSK.lock.release }
+
+        MRSK.holding_lock = false
+      end
+
+      def hold_lock_on_error
+        if MRSK.hold_lock_on_error?
+          yield
+        else
+          MRSK.hold_lock_on_error = true
+          yield
+          MRSK.hold_lock_on_error = false
         end
       end
   end