Changes to work with security 3.1

Changes to password hashing work to work with changes made in security
3.1 for thread-safety
Call runRead, not runWrite

SecurityXmlUserManager getUserRoles and searchUsers are read-based
methods, but are calling runWrite to run their actions. Acquiring a
write lock for these operations is unnecessary. They should be calling
runRead
Merge pull request #30 from sonatype/security-concurrency-bug

REVIEW: Call runRead, not runWrite
Merge remote-tracking branch 'origin/master' into NXCM-4361-salt-rework
Rename default password service, as it is not nexus-specific