Use Regexp literals in validations

We used to store regular expressions as strings in the validations.rb which
causes them to be compiled every time the validation is run. With this commit
we are changing them to be stored as Regexp objects which are compiled only
once at the load time.

lib/validation.rb

@@ -16,19 +16,19 @@ def initialize(details)
   # - Not start or end with a hyphen
   # Adapted from https://stackoverflow.com/a/7933253
   # Do not allow uppercase letters to not deal with case sensitivity
-  ALLOWED_NAME_PATTERN = '\A[a-z0-9](?:[a-z0-9\-]{0,61}[a-z0-9])?\z'
+  ALLOWED_NAME_PATTERN = %r{\A[a-z0-9](?:[a-z0-9\-]{0,61}[a-z0-9])?\z}
 
   # Different operating systems have different conventions.
   # Below are reasonable restrictions that works for most (all?) systems.
   # - Max length 32
   # - Only lowercase letters, numbers, hyphens and underscore
   # - Not start with a hyphen or number
-  ALLOWED_OS_USER_NAME_PATTERN = '\A[a-z_][a-z0-9_-]{0,31}\z'
+  ALLOWED_OS_USER_NAME_PATTERN = %r{\A[a-z_][a-z0-9_-]{0,31}\z}
 
   # Minio user name, we are using ALLOWED_OS_USER_NAME_PATTERN with min length of 3
-  ALLOWED_MINIO_USERNAME_PATTERN = '\A[a-z_][a-z0-9_-]{2,31}\z'
+  ALLOWED_MINIO_USERNAME_PATTERN = %r{\A[a-z_][a-z0-9_-]{2,31}\z}
 
-  ALLOWED_PORT_RANGE_PATTERN = '\A(\d+)(?:\.\.(\d+))?\z'
+  ALLOWED_PORT_RANGE_PATTERN = %r{\A(\d+)(?:\.\.(\d+))?\z}
 
   # - Max length 63
   # - Alphanumeric, hyphen, underscore, space, parantheses, exclamation, question mark, star