Add documentation and minor style changes

Add doxygen style documentation to `mbedtls_test_fail`, `mbedtls_test_skip`,
`mbedtls_test_set_step` and `mbedtls_test_info_reset`. This should make it
easier to understand how the test infrastructure is used.

Also make some minor style changes to meet the coding standards and make it
more obvious that `mbedtls_test_info.step` was being incremented.

Signed-off-by: Chris Jones <christopher.jones@arm.com>
diff --git a/tests/suites/host_test.function b/tests/suites/host_test.function
index f345408..3138c33 100644
--- a/tests/suites/host_test.function
+++ b/tests/suites/host_test.function
@@ -601,7 +601,7 @@
     }
 
     /* Initialize the struct that holds information about the last test */
-    mbedtls_test_info_reset();
+    mbedtls_test_info_reset( );
 
     /* Now begin to execute the tests in the testfiles */
     for ( testfile_index = 0;
@@ -683,7 +683,7 @@
             // If there are no unmet dependencies execute the test
             if( unmet_dep_count == 0 )
             {
-                mbedtls_test_info_reset();
+                mbedtls_test_info_reset( );
 
 #if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
                 /* Suppress all output from the library unless we're verbose