Add --cpus flag to control cpu resources

This fix tries to address the proposal raised in 27921 and add
`--cpus` flag for `docker run/create`.

Basically, `--cpus` will allow user to specify a number (possibly partial)
about how many CPUs the container will use. For example, on a 2-CPU system
`--cpus 1.5` means the container will take 75% (1.5/2) of the CPU share.

This fix adds a `NanoCPUs` field to `HostConfig` since swarmkit alreay
have a concept of NanoCPUs for tasks. The `--cpus` flag will translate
the number into reused `NanoCPUs` to be consistent.

This fix adds integration tests to cover the changes.

Related docs (`docker run` and Remote APIs) have been updated.

This fix fixes 27921.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

man/docker-create.1.md

@@ -19,6 +19,7 @@ docker-create - Create a new container
 [**--cpu-quota**[=*0*]]
 [**--cpu-rt-period**[=*0*]]
 [**--cpu-rt-runtime**[=*0*]]
+[**--cpus**[=*0.0*]]
 [**--cpuset-cpus**[=*CPUSET-CPUS*]]
 [**--cpuset-mems**[=*CPUSET-MEMS*]]
 [**--device**[=*[]*]]
@@ -154,6 +155,9 @@ two memory nodes.
 
    The sum of all runtimes across containers cannot exceed the amount allotted to the parent cgroup.
 
+**--cpus**=0.0
+   Number of CPUs. The default is *0.0*.
+
 **--device**=[]
    Add a host device to the container (e.g. --device=/dev/sdc:/dev/xvdc:rwm)
 

man/docker-run.1.md

@@ -19,6 +19,7 @@ docker-run - Run a command in a new container
 [**--cpu-quota**[=*0*]]
 [**--cpu-rt-period**[=*0*]]
 [**--cpu-rt-runtime**[=*0*]]
+[**--cpus**[=*0.0*]]
 [**--cpuset-cpus**[=*CPUSET-CPUS*]]
 [**--cpuset-mems**[=*CPUSET-MEMS*]]
 [**-d**|**--detach**]
@@ -208,6 +209,9 @@ to the quota you specify.
 
    The sum of all runtimes across containers cannot exceed the amount allotted to the parent cgroup.
 
+**--cpus**=0.0
+   Number of CPUs. The default is *0.0* which means no limit.
+
 **-d**, **--detach**=*true*|*false*
    Detached mode: run the container in the background and print the new container ID. The default is *false*.