(MODULES-1338) Allow mysql::db to import several files

A user might need to import several files on database creation.
Currently the module only allows the import of a single file.
This commit allows one to, from now on, import severals.

Before :

  mysql::db { 'test' :
    sql => '/tmp/my_import1.sql',
  }

Now :

  mysql::db { 'test' :
    sql => [
      '/tmp/my_import1.sql',
      '/tmp/my_import2.sql',
    ]
  }
Fix regression in username validation

Commit cdd7132ff9c3a8ac63621899f1e82bdd0ec58974 added logic to catch invalid database usernames,
but the regex it uses fails to match usernames with special characters that are properly quoted,
causing errors with usernames that used to work in versions < 3.0.0. This fixes the regex so that
if the username is quoted, anything is allowed between the quotes.

From the docs (http://dev.mysql.com/doc/refman/5.5/en/identifiers.html):
"Permitted characters in quoted identifiers include the full Unicode Basic Multilingual Plane (BMP),
except U+0000"
Merge pull request #602 from theasci/fix-user-validation-regression

Fix regression in username validation
Merge pull request #574 from Mylezeem/allow_multiple_import_at_a_time

(MODULES-1338) Allow mysql::db to import several files
Fix test issues

Remove the dependency on stdlib 4.x puppetlabs/puppetlabs-mysql#574
introduced, add some input validation, and improve test checks.
Merge pull request #603 from mhaskel/mysql_test_fixes

Fix test issues