* Refactoring

* Fix issue that causes a new image store to be created at every start of ucloud-api.
* VM Migration API call now takes hostname instead of host key.
* StorageHandler Classes are introduced. They transparently handles things related to importing of image, make vm out of image, resize vm image, delete vm image etc.
* Loggers added to __init__.py of every ucloud component's subpackage.
* Non-Trivial Timeout Events are no longer logged.
* Fix issue that prevents removal of stopped VMs (i.e VMs that are successfully migrated).
* Improved unit handling added. e.g MB, Mb, mB, mb are all Mega Bytes.
* VM migration is now possible on IPv6 host.
* Destination VM (receiving side of migration of a vm) now correctly expects incoming data on free ephemeral port.
* Traceback is no longer output to screen, instead it goes to log file.
* All sanity checks are put into a single file. These checks are run by ucloud.py before running any of ucloud component.

sanity_checks.py

@@ -0,0 +1,33 @@
+import sys
+import subprocess as sp
+
+from os.path import isdir
+from config import env_vars
+
+
+def check():
+    #########################
+    #  ucloud-image-scanner #
+    #########################
+    if env_vars.get('STORAGE_BACKEND') == 'filesystem' and not isdir(env_vars.get('IMAGE_DIR')):
+        print("You have set STORAGE_BACKEND to filesystem. So,"
+              "the {} must exists. But, it don't".format(env_vars.get('IMAGE_DIR')))
+        sys.exit(1)
+
+    try:
+        sp.check_output(['which', 'qemu-img'])
+    except Exception:
+        print("qemu-img missing")
+        sys.exit(1)
+
+    ###############
+    # ucloud-host #
+    ###############
+
+    if env_vars.get('STORAGE_BACKEND') == 'filesystem' and not isdir(env_vars.get('VM_DIR')):
+        print("You have set STORAGE_BACKEND to filesystem. So, the vm directory mentioned"
+              " in .env file must exists. But, it don't.")
+        sys.exit(1)
+
+if __name__ == "__main__":
+    check()