update EnvironmentCredential and azure.core.util.Configuration#7337

Merged

alzimmermsft merged 8 commits intoAzure:Identity-ENVVARsfrom cxznmhdcxz:Identity-ENVVARs

Jan 28, 2020

+91-14

Commits on Jan 10, 2020

update EnvironmentCredentail, azure.core.utils.Configuration
cxznmhdcxz
committed

Commits on Jan 13, 2020

added tests to EnvironmentCredentialTests
cxznmhdcxz
committed

Commits on Jan 17, 2020

added a method to determine multiple configurations exist, updated EnvironmentCredential
cxznmhdcxz
committed

Commits on Jan 23, 2020

update javadoc comments for EnvironmentCredential
cxznmhdcxz
committed