RFR: JDK-8138574: [TESTBUG] TestBasicLogOutput.java doesn't account for padding

[Rachel Protacio]

Hello! Please review this one-character change to fix bug 8138574, where 
the existing test was not general enough to pass as new logging tags are 
added.

Summary: TestBasicLogOutput.java edited to account for padding in tag 
descriptors

Bug: https://bugs.openjdk.java.net/browse/JDK-8138574
Webrev: http://cr.openjdk.java.net/~coleenp/8138574

Testing: passes jtreg on own and when tested with added tags

Thank you,
Rachel