Remove truncate error log from rocksdb.rocksdb_checksums test

Upstream commit ID : fb-mysql-5.6.35/f0cbe47e1b2dcdc8f8f9ca89f6b0fc8faab85e17
PS-4476 : Merge prod--------

Summary:
Restart the test using a new error log instead of truncating the old
error log. Also reduce the number of rows from 10000 to 4000 to speed up
the test.

Reviewed By: asandryh

Differential Revision: D7003203

fbshipit-source-id: 6b830ce

mysql-test/suite/rocksdb/r/rocksdb_checksums.result

@@ -37,9 +37,6 @@ create table t4 (pk int primary key, a int, b int, key(a), key(b)) engine=rocksd
 check table t4;
 Table	Op	Msg_type	Msg_text
 rocksdb_checksums_test.t4	check	status	OK
-10000 index entries had around 500 checksums
-10000 index entries had around 500 checksums
-Around 500 table records had checksums
 set session rocksdb_checksums_pct=100;
 #
 # Ok, table t2 has all rows with checksums. Simulate a few checksum mismatches.

mysql-test/suite/rocksdb/t/rocksdb_checksums.test

@@ -84,7 +84,7 @@ create table t4 (pk int primary key, a int, b int, key(a), key(b)) engine=rocksd
 --disable_query_log
 let $i=0;
 let $x= 100000;
-while ($i<10000)
+while ($i<4000)
 {
   inc $i;
   eval insert t4(pk,a,b) values($i, $i, $i div 10);