Fix kv parsing bug in greentea client.

Mbed greentea sends all KV pairs in the following format:
"{{key,value}}\n"
Previously the greentea client code was not reading the final '\n' from
the UART as part of the HandleKV() call. This did not cause an
error when multiple KV pairs were being parsed because any whitespace
proceeding a message was ignored. Once the final KV pair was sent,
however, HandleKV() would only read up to the "}}" leaving the final
'\n' in the UART buffer.

Author: dustin-crossman

features/frameworks/greentea-client/source/greentea_test_env.cpp

@@ -523,7 +523,7 @@ static int CurTok = 0;
  *
  *        tok_eof       ::= EOF (end of file)
  *        tok_open      ::= "{{"
- *        tok_close     ::= "}}"
+ *        tok_close     ::= "}}\n"
  *        tok_semicolon ::= ";"
  *        tok_string    ::= [a-zA-Z0-9_-!@#$%^&*()]+    // See isstring() function
  *
@@ -597,7 +597,7 @@ extern "C" int greentea_parse_kv(char *out_key,
 
         case tok_open:
             if (HandleKV(out_key, out_value, out_key_size, out_value_size)) {
-                // We've found {{ KEY ; VALUE }} expression
+                // We've found {{ KEY ; VALUE }}\n expression
                 return 1;
             }
             break;
@@ -684,7 +684,7 @@ static int isstring(int c) {
  *
  *         <TOK_EOF>       ::= EOF (end of file)
  *         <TOK_OPEN>      ::= "{{"
- *         <TOK_CLOSE>     ::= "}}"
+ *         <TOK_CLOSE>     ::= "}}\n"
  *         <TOK_SEMICOLON> ::= ";"
  *         <TOK_STRING>    ::= [a-zA-Z0-9_-!@#$%^&*()]+    // See isstring() function *
  *
@@ -737,13 +737,16 @@ static int gettok(char *out_str, const int str_size) {
     }
 
     // close ::= '}'
-	if (LastChar == '}') {
-		LastChar = greentea_getc();
-		if (LastChar == '}') {
-			LastChar = '!';
-			return tok_close;
-		}
-	}
+    if (LastChar == '}') {
+        LastChar = greentea_getc();
+        if (LastChar == '}') {
+            LastChar = greentea_getc();
+            if (LastChar == '\n') {
+                LastChar = '!';
+                return tok_close;
+            }
+        }
+    }
 
     if (LastChar == EOF)
         return tok_eof;
@@ -762,8 +765,8 @@ static int gettok(char *out_str, const int str_size) {
  *         <MESSAGE>: <TOK_OPEN> <TOK_STRING> <TOK_SEMICOLON> <TOK_STRING> <TOK_CLOSE>
  *
  *         Examples:
- *         message:     "{{__timeout; 1000}}"
- *                      "{{__sync; 12345678-1234-5678-1234-567812345678}}"
+ *         message:     "{{__timeout; 1000}}\n"
+ *                      "{{__sync; 12345678-1234-5678-1234-567812345678}}\n"
  *
  *  \param out_key Output buffer to store key string value
  *  \param out_value Output buffer to store value string value