Adding force_flash functionality

aosp/2452605 might've accidentally omitted force flash functionality
from fastboot. Some users need to flash dynamic partitions from
bootloader, so we are readding this feature back into fastboot

Test: adb reboot bootloader, fastboot flash system --force

Change-Id: I37a51ebbe38b27ed428c38068d30c0febd7db09c
diff --git a/fastboot/task.cpp b/fastboot/task.cpp
index bf64f0e..146064c 100644
--- a/fastboot/task.cpp
+++ b/fastboot/task.cpp
@@ -32,7 +32,7 @@
 
 void FlashTask::Run() {
     auto flash = [&](const std::string& partition) {
-        if (should_flash_in_userspace(partition) && !is_userspace_fastboot()) {
+        if (should_flash_in_userspace(partition) && !is_userspace_fastboot() && !fp_->force_flash) {
             die("The partition you are trying to flash is dynamic, and "
                 "should be flashed via fastbootd. Please run:\n"
                 "\n"