Fix metrics test and fix faulty CI (#420)

Just before releasing 1.0.0, I was looking at the running CI integration
tests action. Suddenly, I saw a test failing. **Yet then the CI run
succeeded**!

We discovered that the make recipe for running integration tests, which
is used by the CI, keeps running even if some earlier subcommand in that
recipe, including the main part of integration tests run under valgrind,
fails with a nonzero code.
The culprit was found to be `.ONESHELL` directive on top of the
Makefile, combined with lack of the `-e` option set in the run shells.
Adding `-e` option to `.SHELLFLAGS` fixed the issue.

The test (from MetricsTest) was failing due to recent change in Rust
Driver. Adjusting it was trivial.

## Pre-review checklist

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- [x] I have split my patch into logically separate commits.
- [x] All commit messages clearly explain what they change and why.
- [x] PR description sums up the changes and reasons why they should be
introduced.
- ~~[ ] I have implemented Rust unit tests for the features/changes
introduced.~~
- ~~[ ] I have enabled appropriate tests in `Makefile` in
`{SCYLLA,CASSANDRA}_(NO_VALGRIND_)TEST_FILTER`.~~
- ~~[ ] I added appropriate `Fixes:` annotations to PR description.~~

Author: wprzytula

Makefile

@@ -3,9 +3,10 @@ SPACE := ${EMPTY} ${EMPTY}
 .ONESHELL:
 
 SHELL := bash
+.SHELLFLAGS := -ec
 ifeq ($(OS),Windows_NT)
     SHELL := pwsh.exe
-    .SHELLFLAGS := -NoProfile -Command
+    .SHELLFLAGS := -NoProfile -Command $$ErrorActionPreference = 'Stop';
 endif
 
 UNAME_S := $(shell uname -s)

tests/src/integration/tests/test_metrics.cpp

@@ -47,18 +47,16 @@ CASSANDRA_INTEGRATION_TEST_F(MetricsTests, StatsConnections) {
                         .with_constant_reconnect(10)
                         .connect(); // low reconnect for faster node restart
 
-  // All expected values are greater by 1 than in cpp-driver.
-  // This is caused by Rust Driver including Control Connection in the metrics.
   CassMetrics metrics = session.metrics();
-  EXPECT_EQ(3u, metrics.stats.total_connections);
+  EXPECT_EQ(2u, metrics.stats.total_connections);
 
   stop_node(1);
   metrics = session.metrics();
-  EXPECT_EQ(2u, metrics.stats.total_connections);
+  EXPECT_EQ(1u, metrics.stats.total_connections);
 
   start_node(1);
   metrics = session.metrics();
-  EXPECT_EQ(3u, metrics.stats.total_connections);
+  EXPECT_EQ(2u, metrics.stats.total_connections);
 }
 
 /**