Rename globals to avoid shadowing by various function arguments

It's easier and more telling to rename the globals used only for test,
rather than rename all the shadowing function arguments.
diff --git a/library/pkcs5.c b/library/pkcs5.c
index 5013343..86ab3e7 100644
--- a/library/pkcs5.c
+++ b/library/pkcs5.c
@@ -304,10 +304,10 @@
 
 #define MAX_TESTS   6
 
-static const size_t plen[MAX_TESTS] =
+static const size_t plen_test_data[MAX_TESTS] =
     { 8, 8, 8, 24, 9 };
 
-static const unsigned char password[MAX_TESTS][32] =
+static const unsigned char password_test_data[MAX_TESTS][32] =
 {
     "password",
     "password",
@@ -316,10 +316,10 @@
     "pass\0word",
 };
 
-static const size_t slen[MAX_TESTS] =
+static const size_t slen_test_data[MAX_TESTS] =
     { 4, 4, 4, 36, 5 };
 
-static const unsigned char salt[MAX_TESTS][40] =
+static const unsigned char salt_test_data[MAX_TESTS][40] =
 {
     "salt",
     "salt",
@@ -380,8 +380,8 @@
         if( verbose != 0 )
             mbedtls_printf( "  PBKDF2 (SHA1) #%d: ", i );
 
-        ret = mbedtls_pkcs5_pbkdf2_hmac( &sha1_ctx, password[i], plen[i], salt[i],
-                                  slen[i], it_cnt[i], key_len[i], key );
+        ret = mbedtls_pkcs5_pbkdf2_hmac( &sha1_ctx, password_test_data[i], plen_test_data[i], salt_test_data[i],
+                                  slen_test_data[i], it_cnt[i], key_len[i], key );
         if( ret != 0 ||
             memcmp( result_key[i], key, key_len[i] ) != 0 )
         {