Add new module to store the progress

This module is used to store the progress of the bootstrap process and
could be used by other applications to get status of virt-bootstrap as
well as percentage of completion.

Convert some info messages to use this new system for a clean reporting
in client applications.

Example usage:

    import virtBootstrap

    def show_progress(data):
        print("Status: %s, Progress: %.2f"
              % (data['status'], data['value']))

    virtBootstrap.bootstrap(uri='docker://ubuntu', dest="/tmp/test1",
                            progress_cb=show_progress)

1 files changed, 67 insertions, 0 deletions

diff --git a/src/virtBootstrap/progress.py b/src/virtBootstrap/progress.py
new file mode 100644
index 0000000..3463168
--- /dev/null
+++ b/src/virtBootstrap/progress.py
@@ -0,0 +1,67 @@
+# Authors:
+#   Cedric Bosdonnat <cbosdonnat@suse.com>
+#   Radostin Stoyanov <rstoyanov1@gmail.com>
+#
+# Copyright (c) 2017 Radostin Stoyanov
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""
+Store the progress of virt-bootstrap
+"""
+
+
+class Progress(object):
+    """
+    Store progress status and value of virt-bootstrap and
+    inform callback method about change.
+    """
+
+    def __init__(self, callback=None):
+        """
+        If callback method is passed it will be called when the progress
+        value has been changed.
+        """
+        self.progress = {'status': '', 'value': 0}
+        self.callback = callback
+
+    def get_progress(self):
+        """
+        Return "state" and "value" of the progress in python dictionary.
+        """
+        return self.progress.copy()
+
+    def update_progress(self, status=None, value=None, logger=None):
+        """
+        Set status/value and call the callback method if available.
+        Log information message if logger instance was passed.
+
+        @param status: String representing the current state of virt-bootstrap.
+        @param value: The new progress value of virt-bootstrap.
+        @param logger: Reference to logger. If passed info message with
+                       including the status will be logged.
+        """
+        # Note: We do not validate the values stored in progress
+        if isinstance(status, str):
+            self.progress['status'] = status
+        if isinstance(value, (float, int)):
+            self.progress['value'] = value
+
+        try:
+            if logger is not None:
+                logger.info(status)
+            if self.callback is not None:
+                self.callback(self.get_progress())
+        except Exception as err:
+            raise ValueError("Progress update has failed.", err)