JaCoCo not generating jacoco.exec until after skipping JaCoCo execution

Just an addition to the answers already given.
It could happen that in your maven-surefire-plugin configuration you already use the argLine configuration to override something like the memory used. If you do so the argline set by jacoco-maven-plugin will not be used failing to generate the jacoco report.
In this case assign a property name to the jacoco-maven-plugin config and then reference it in your maven-surefire-plugin argLine parameter.

        <plugin>
            <groupId>org.jacoco</groupId>
            <artifactId>jacoco-maven-plugin</artifactId>
            <version>0.7.9</version>
            <executions>
                <!-- prepare agent for measuring unit tests -->
                <execution>
                    <id>prepare-unit-tests</id>
                    <goals>
                        <goal>prepare-agent</goal>
                    </goals>
                    <configuration>
                        <append>true</append>
                        <destFile>${sonar.jacoco.reportPath}</destFile>
                        <!-- Sets the VM argument line used when unit tests are run. -->
                        <propertyName>surefireArgLine</propertyName>
                    </configuration>
                </execution>
            </executions>
        </plugin>

[…]

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-surefire-plugin</artifactId>
            <version>2.19.1</version>
            <configuration>
                <printSummary>false</printSummary>
                <redirectTestOutputToFile>true</redirectTestOutputToFile>
                <forkCount>3</forkCount>
                <reuseForks>true</reuseForks>
                <argLine>${surefireArgLine} -Xmx1024m -noverify</argLine>                  
            </configuration>
        </plugin>