Fixes #10457-Pause-and-unpause-accept-multi-containers

Applied multi parameters to pause and unpause.
Created a new test file dedicated for pause commands.
Created a new utility function to get a slice of paused containers.
Updated documentation

Signed-off-by: André Martins <martins@noironetworks.com>

docs/man/docker-pause.1.md

@@ -6,7 +6,7 @@ docker-pause - Pause all processes within a container
 
 # SYNOPSIS
 **docker pause**
-CONTAINER
+CONTAINER [CONTAINER...]
 
 # DESCRIPTION
 

docs/man/docker-unpause.1.md

@@ -6,7 +6,7 @@ docker-unpause - Unpause all processes within a container
 
 # SYNOPSIS
 **docker unpause**
-CONTAINER
+CONTAINER [CONTAINER...]
 
 # DESCRIPTION
 

docs/sources/reference/commandline/cli.md

@@ -1359,7 +1359,7 @@ nano-second part of the timestamp will be padded with zero when necessary.
 
 ## pause
 
-    Usage: docker pause CONTAINER
+    Usage: docker pause CONTAINER [CONTAINER...]
 
     Pause all processes within a container
 
@@ -1396,22 +1396,6 @@ just a specific mapping:
     $ sudo docker port test 7890
     0.0.0.0:4321
 
-## pause
-
-    Usage: docker pause CONTAINER
-
-    Pause all processes within a container
-
-The `docker pause` command uses the cgroups freezer to suspend all processes in
-a container.  Traditionally when suspending a process the `SIGSTOP` signal is
-used, which is observable by the process being suspended. With the cgroups freezer
-the process is unaware, and unable to capture, that it is being suspended,
-and subsequently resumed.
-
-See the
-[cgroups freezer documentation](https://www.kernel.org/doc/Documentation/cgroups/freezer-subsystem.txt)
-for further details.
-
 ## rename
 
     Usage: docker rename OLD_NAME NEW_NAME
@@ -2081,7 +2065,7 @@ them to [*Share Images via Repositories*](
 
 ## unpause
 
-    Usage: docker unpause CONTAINER
+    Usage: docker unpause CONTAINER [CONTAINER...]
 
     Unpause all processes within a container