Do not use .netrc implicitly if no CredentialsProvider was set

Do not silently set the NetRCCredentialsProvider if no
CredentialsProvider was set explicitly since applications may want to
have full control which provider should be used.

Bug: 444338
Change-Id: Ie096983bc1caa90443a504d302bfea8f2d26ab9e
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
[Java 8] Configure doclint to accept missing descriptions

We avoid trivial descriptions in JavaDoc. Hence configure
doclint to not fail on missing descriptions.

Change-Id: Iba3d5aec18cc7d7f43e53fa6789f0dede9996fb7
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Add chaining credentials provider

The chaining credentials provider sequentially tries to obtain
credentials from a list of credential providers and returns the
credentials from the first provider which can provide them.

Change-Id: I499f304119d7066d011dbde3556dee6facee8ab0
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
[cli] Use chaining credentials provider to enable .netrc

If available use credentials in .netrc otherwise prompt the user
if jgit command line needs credentials for remote operations.

Change-Id: Iea1f595618edfb87a37137db08bac8ca2d500ebc
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Merge remote-tracking branch 'remotes/upstream/stable-3.5' into stable