make roles initializers idempotent

contracts/access/roles/CapperRole.sol

@@ -13,8 +13,10 @@ contract CapperRole is Initializable {
   Roles.Role private cappers;
 
   function initialize() public initializer {
+    if (!isCapper(msg.sender)) {
       _addCapper(msg.sender);
     }
+  }
 
   modifier onlyCapper() {
     require(isCapper(msg.sender));

contracts/access/roles/MinterRole.sol

@@ -13,8 +13,10 @@ contract MinterRole is Initializable {
   Roles.Role private minters;
 
   function initialize() public initializer {
+    if (!isMinter(msg.sender)) {
       _addMinter(msg.sender);
     }
+  }
 
   modifier onlyMinter() {
     require(isMinter(msg.sender));

contracts/access/roles/PauserRole.sol

@@ -13,8 +13,10 @@ contract PauserRole is Initializable {
   Roles.Role private pausers;
 
   function initialize() public initializer {
+    if (!isPauser(msg.sender)) {
       _addPauser(msg.sender);
     }
+  }
 
   modifier onlyPauser() {
     require(isPauser(msg.sender));

contracts/access/roles/SignerRole.sol

@@ -13,8 +13,10 @@ contract SignerRole is Initializable {
   Roles.Role private signers;
 
   function initialize() public initializer {
+    if (!isSigner(msg.sender)) {
       _addSigner(msg.sender);
     }
+  }
 
   modifier onlySigner() {
     require(isSigner(msg.sender));