make executable, vote and stake account rent exempt (#6017)

* add missing convenience method

* require vote account to be exempt

* make stake account rent exempt

* making executable rent exempt

* rent will be initialized in genesis

* add test for update_rent

sdk/src/loader_instruction.rs

@@ -1,5 +1,6 @@
 use crate::instruction::{AccountMeta, Instruction};
 use crate::pubkey::Pubkey;
+use crate::sysvar::rent;
 
 #[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
 pub enum LoaderInstruction {
@@ -15,6 +16,7 @@ pub enum LoaderInstruction {
     /// bit of the Account
     ///
     /// * key[0] - the account to prepare for execution
+    /// * key[1] - rent sysvar account
     ///
     /// The transaction must be signed by key[0]
     Finalize,
@@ -40,6 +42,9 @@ pub fn write(
 }
 
 pub fn finalize(account_pubkey: &Pubkey, program_id: &Pubkey) -> Instruction {
-    let account_metas = vec![AccountMeta::new(*account_pubkey, true)];
+    let account_metas = vec![
+        AccountMeta::new(*account_pubkey, true),
+        AccountMeta::new(rent::id(), false),
+    ];
     Instruction::new(*program_id, &LoaderInstruction::Finalize, account_metas)
 }