Add external package management support

Add external package management support

Some methods are added to manage external packages:
  'PrepareLib': checks the existence of an external library, if it
doesn't exist, calls the script user provided to download(if required)
and build the source code of the external library or notify user to
install the library.
  'Download': download package from specify URL
  'UnpackAll': unpack the package
  'Configure': execute specify script(configure, bootstrap etc)
  'InstallHeadFile': install head files
  'InstallLib': install library binaries(.so, .a etc)

Change-Id: Ibf3ef58abf8ba5a466b82a341bb6dce83d61726e
Signed-off-by: Caiwen Zhang<caiwen.zhang@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/138
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Patrick Lankswert <patrick.lankswert@intel.com>