Change implementation of string splitting to support zero-length components

Change implementation of string splitting to support zero-length components

Previous code responsible from splitting a space-separated string used
stringstream for this purpose. If one of the components used to create such
string was empty, it resulted in two consecutive spaces that were "swallowed"
by stringstream.

Now the string is parsed using std::string::find method to manually detect
locations of delimiting spaces and cut the string to pieces.

Change-Id: I2aa964716f0d41f13807bbef5c8aab6c55715a34
Signed-off-by: Rafal Krypa <r.krypa@samsung.com>