(PUP-11993) Style/UnpackFirst

This commit enables the Style/UnpackFirst cop and fixes 5
autocorrectable offenses.

Author: AriaXLi

.rubocop_todo.yml

@@ -762,13 +762,6 @@ Style/TrailingUnderscoreVariable:
 Style/TrivialAccessors:
   Enabled: false
 
-# This cop supports safe auto-correction (--auto-correct).
-Style/UnpackFirst:
-  Exclude:
-    - 'lib/puppet/file_serving/http_metadata.rb'
-    - 'lib/puppet/provider/nameservice/directoryservice.rb'
-    - 'lib/puppet/provider/user/directoryservice.rb'
-
 # This cop supports safe auto-correction (--auto-correct).
 Style/VariableInterpolation:
   Exclude:

lib/puppet/file_serving/http_metadata.rb

@@ -20,7 +20,7 @@ def initialize(http_response, path = '/dev/null')
     checksum = http_response['content-md5']
     if checksum
       # convert base64 digest to hex
-      checksum = checksum.unpack("m").first.unpack("H*").first
+      checksum = checksum.unpack1("m").unpack1("H*")
       @checksums[:md5] = "{md5}#{checksum}"
     end
 

lib/puppet/provider/nameservice/directoryservice.rb

@@ -264,7 +264,7 @@ def self.get_password(guid, username)
         # string. The password_hash provided as a resource attribute is a
         # hex value. We need to convert the Base64 encoded string to a
         # hex value and provide it back to Puppet.
-        converted_hash_plist['SALTED-SHA512'].unpack("H*")[0]
+        converted_hash_plist['SALTED-SHA512'].unpack1("H*")
 
       end
     end

lib/puppet/provider/user/directoryservice.rb

@@ -205,7 +205,7 @@ def self.convert_binary_to_hash(plist_data)
   # The salted-SHA512 password hash in 10.7 is stored in the 'SALTED-SHA512'
   # key as binary data. That data is extracted and converted to a hex string.
   def self.get_salted_sha512(embedded_binary_plist)
-    embedded_binary_plist['SALTED-SHA512'].unpack("H*")[0]
+    embedded_binary_plist['SALTED-SHA512'].unpack1("H*")
   end
 
   # This method reads the passed embedded_binary_plist hash and returns values
@@ -220,7 +220,7 @@ def self.get_salted_sha512_pbkdf2(field, embedded_binary_plist, user_name = "")
         raise Puppet::Error, "Invalid #{field} given for user #{user_name}"
       end
 
-      value.unpack('H*').first
+      value.unpack1('H*')
     when 'iterations'
       Integer(embedded_binary_plist['SALTED-SHA512-PBKDF2'][field])
     else