ACCUMULO-2058 Add shell env interpolation for ACCUMULO_CONF_DIR when extracting kerberos keytab value.
Merge branch '1.4.5-SNAPSHOT' into 1.5.1-SNAPSHOT

Conflicts:
	core/src/main/java/org/apache/accumulo/core/security/SecurityUtil.java
Merge branch '1.5.1-SNAPSHOT' into 1.6.0-SNAPSHOT

Conflicts:
	core/src/main/java/org/apache/accumulo/core/security/SecurityUtil.java

1.6 should already interpolate correctly due to changes in Property and AccumuloConfiguration.