Refactor and optimize code

[rvelaVenafi]

@warrior-abhijit has suggested several changes to vcert-python code. We can address them together in one issue.

switch case will be better here ?
Originally posted by @warrior-abhijit in #41 (comment)

address todo now ?? as these are lot of if, else in here
Originally posted by @warrior-abhijit in #41 (comment)

regex match API would be lot better here and will remove lot of duplicate code below w.r.t regex match
Originally posted by @warrior-abhijit in #41 (comment)

switch case may be here as well ?
Originally posted by @warrior-abhijit in #41 (comment)

There is a handy Python wrapper called @Property. This can be handy here. It would look like this:
@Property
def base_url(self):
# This is a getter
return self._base_url

@base_url.setter
def base_url(self, value):
# This is the setter method
self._base_url = self._normalize_and_verify_base_url(value)

It's nicer for refactoring and is pretty explicit.
Originally posted by @HELGAHR in #41 (comment)

How safe is it in this method to assume that these dictionary keys resolve? I'm new to this code, but I usually think thrice before trying to access a node in the dictionary without .get().
Originally posted by @HELGAHR in #41 (comment)

Just a tidbit of input: Python string objects have a .startswith() method that's easier to read than a regex, although a regex works fine.
Originally posted by @HELGAHR in #41 (comment)

No use in having a doc string if the parameters aren't described, IMO.
Originally posted by @HELGAHR in #41 (comment)