Add multiple vms disk error_policy test cases.
Change unhotplug to coldplug.
Test shableable block disk on 2 domains.
Fix pool related cases to recover selinux state.

This commit is base on a virt-test change to recover selinux state
after creating an NFS pool. Besides this change, this commit also
fixed a few bugs.
1) Stop virsh.domblkerror cleanup entire temp directory.
2) Clean virsh.vol_create_from and virsh.vol_download_upload file.
3) Create the file before chmod in virsh.vol_download_upload to
   prevent error.

Signed-off-by: Hao Liu <hliu@redhat.com>
Move some common functions to utils_test.libvirt.py
Change fs creation method to utils_test.libvirt.mkfs/mk_part.
Modify iscsi device creation method.
Fix a bug of report error policy.
Add test cases for disk encryption option.
Remove a debug line.
Modify fs creation method according to utils_test module.
Modify pool and vol creation method.
Modify vol_create function to check virsh command return code.
Check parted command in guest before using it.
Add more debug info when vm failed to start.
Use small disk size.
Improved the code implementation.
Merge pull request #199 from rbian/error-policy

Add disk error_policy test cases.
Merge pull request #179 from rbian/disk-encryption

Disk encryption test cases.
Merge pull request #226 from Hao-Liu/fix_selinux_recover

Fix pool related cases to recover selinux state.