It took me awhile and lots of Googling to figure this one out. For some reason qemu-img could not convert the .vmdk file into .img. What I did was converted the .vmdk file into .vdi using VirtualBox. Then when I got the .vdi file, I use the qemu-img to convert it to .img.
This is the command
nixmbpr:~ Karlo$ cd /Applications/GNS3.app/Contents/Resources/qemu/bin/ nixmbpr:~ Karlo$ sudo ./qemu-img convert -O qcow2 /Users/Karlo/GNS3/images/junos-vsrx-12.1X47-D15.4/junos-vsrx-12.1X47-D15.4-domestic-disk1.vdi /Users/Karlo/GNS3/images/junos-vsrx-12.1X47-D15.4/junos-vsrx-12.1X47-D15.4-domestic-disk1.img
Once you get the .img, you can add it to GNS3. Make sure you navigate to GNS3 > Preferences > QEMU > QEMU VMs > (select your vsrx) > Edit > Advance Settings. Under Options, change the default options -vga none -vnc none to –smp -2
By changing the options, qemu should recognize the interfaces otherwise you won’t see any physical interface.
The only thing that sucks about running the vSRX via qemu is the boot time is very slow compare to VirtualBox. VirtualBox is fast, I mean really fast boot time.