Show pop-up message when fail to remove VM directory.

Show pop-up message when fail to remove VM directory.

- When user try to "delete" VM, VM data directory is not removed occasionally
because some files or directories in VM data directory are being used by other process.
In this case, emulator-manager show warning message. Then user should check and remove
VM data directory completely. If data directory remains, creating a new VM with same name
is impossible.

Change-Id: I2406639a10c72c8365fac02235400abe4fceb9d0
Signed-off-by: minkee.lee <minkee.lee@samsung.com>