Fix github API requests after asset upload (#771)

In the old code the self.__hostname would be overwritten with uploads.github.com
but it could not be correctly re-set to api.github.com after completing the upload
Create a separate connection if hostname or port differ in requestBlobAndCheck

in the end this became quite a large overhaul, to also make this change generic
for e.g. connecting to status.github.com and similar methods

~~not sure if tests need (more) updating, if so I will update the PR accordingly~~

github/tests/ReplayData/ExposeAllAttributes.testAllClasses.txt

@@ -265,7 +265,7 @@ None
 https
 GET
 status.github.com
-443
+None
 /api/status.json
 {'Authorization': 'Basic login_and_password_removed', 'User-Agent': 'PyGithub/Python'}
 None
@@ -276,7 +276,7 @@ None
 https
 GET
 status.github.com
-443
+None
 /api/last-message.json
 {'Authorization': 'Basic login_and_password_removed', 'User-Agent': 'PyGithub/Python'}
 None

github/tests/ReplayData/Status.testGetLastMessage.txt

@@ -1,7 +1,7 @@
 https
 GET
 status.github.com
-443
+None
 /api/last-message.json
 {'Authorization': 'Basic login_and_password_removed', 'User-Agent': 'PyGithub/Python'}
 None

github/tests/ReplayData/Status.testGetMessages.txt

@@ -1,7 +1,7 @@
 https
 GET
 status.github.com
-443
+None
 /api/messages.json
 {'Authorization': 'Basic login_and_password_removed', 'User-Agent': 'PyGithub/Python'}
 None

github/tests/ReplayData/Status.testGetStatus.txt

@@ -1,7 +1,7 @@
 https
 GET
 status.github.com
-443
+None
 /api/status.json
 {'Authorization': 'Basic login_and_password_removed', 'User-Agent': 'PyGithub/Python'}
 None