Calculation formula of CPU usage:
cpu_time = (utime_now + stime_now) - (utime_pre + stime_pre);
CPU usage = cpu_time / time_interval;

Get utime and stime from /proc/qemupid/stat, then we can get cpu_time
by calculate variation of these value over time.
And time_interval represent cpu time interval between two data acquisition.
Signed-off-by: NJiajun Chen <1250062498@qq.com>

Read /proc/qemupid/stat file to refresh process info,
include: parent pid, userspace time, task state and etc.
According to these data, add two display itemsi to vmtop:
S: task state
P: physical processor that task is runnning on
Signed-off-by: NJiajun Chen <1250062498@qq.com>

Merge pull request !1 from nocjj/master

vmtop is a userspace tool which you can run it in host
to help detecting VM's performance.
1. Implement the basic display framework, realize loop display
   and field filter. Press 'f' to enter field filter mode and
   press 'q' to quit.
2. Build compiling project by autotools.
3. Add Mulan license for project.
Signed-off-by: NJiajun Chen <1250062498@qq.com>